In a computer system provided with a plurality of servers, if a failure develops in a server performing an operation (current server), the operation being performed in the current server may be taken over by a backup server so as to increase the availability of the computer system.
An example of such take-over method is a failure recovery method whereby a boot disk (logic unit) having been utilized by the current server experiencing a failure is started up by a backup server running no operation, so that the operation of the current server can be taken over by the backup server. In this method, when there is a plurality of current servers in the computer system, failure recovery is possible no matter which current server fails. Accordingly, high reliability can be obtained by preparing a small number of backup servers for a large number of current servers.
In this method, since the setting of an OS for performing an operation at the time of take-over is minimized, it is preferable to minimize the difference in hardware (H/W) configuration before and after the take-over if high reliability is to be obtained. Particularly, if the H/W configuration is greatly different, take-over may become impossible. In order to eliminate the take-over impossibility, it is necessary to design a dedicated system or OS so that the OS can normally operate even when the H/W configuration is different.
Further, because there are many constraints to physical H/W configuration, in order to match physical computer configurations, it is generally necessary to prepare a computer with an identical H/W configuration. To address such situation, a method may involve constructing a virtual computer, as described in Patent Literature 1. By providing the virtual computer with the identical configuration, the problem of take-over inability due to a different physical configuration is solved.